Drill strings or well strings generally consist of a number of tubular sections (oil field tubulars) connected end-to-end. For some operations and layouts, one-way valves (known in industry as float valves) may be inserted within the well string, for example to allow flow down the string but not up the string. When operational, these valves open to allow fluid to be pumped down the drill string, and close when fluid flow down the drill string stops or if there is reverse flow up the drill string. A higher pressure below the float valve holds the valve closed and fluid or gas is therefore prevented from migrating back up the drill string.
In some situations it may be necessary to convey objects down the drill string on wireline, for example when the drill string has become stuck in the well or when directional surveys are required on wireline. Standard float valves are a barrier in the drill string that prevent wireline access. In stuck pipe scenarios standard float valves add significant difficulty to wireline operations necessary for pipe recovery operations. For directional surveys on wireline the drill string needs to be tripped to surface to remove the standard float valves before wireline operations can begin, this adds significant time and cost to drilling operations. In other situations it may be desirable to deactivate float valves in the drill string to allow reverse circulation.
For the above reasons, at certain times it is desirable to be able to remove the obstruction created by float valves in the drill string. One such device that achieves this is described in WO2014042541. A B-shifting tool assembly is conveyed on slickline that engages a sleeve above a standard float valve and shifts the sleeve into the throat of the valve. A clear path is created allowing tools to be safely conveyed through the valve. Conveying tools on a slickline requires specialist tools that require a specialist slickline contractor to operate. Worn parts or incorrect slickline operation pose a risk in that the slickline tools can prematurely release from the sleeve and become stuck in the float valve. Additional time-consuming operations are required to remedy this situation.
The device described in WO2014042541 utilises a standard float valve. The float valve is contained within a drill string sub, hence the outer diameter of the valve is limited by the geometry allowable through the drill string connection. This in turn limits the diameter of the sleeve that positions within the float valve. The resulting internal diameter of the valve is in some cases too small to allow necessary tools to be conveyed through the valve. The limited ID is also a restriction to flow through the drill string.
It is an object of the present invention to provide a drill string element that helps to overcome the above disadvantages, or which at least provides the public or industry with a useful choice. It is a further object of the present invention to provide an internal sleeve for use with a drill string that helps to overcome the above disadvantages, or which at least provides the public or industry with a useful choice. It is a yet still further object of the present invention to provide a method of activating a drill string float valve that helps to overcome the above disadvantages, or which at least provides the public or industry with a useful choice.